Need .stop in addition to .pause

[arjunguha]

Based on discussion with @joydeep-b . In this state, event handlers are cancelled and discarded.

[joydeep-b]

@arjunguha I've been thinking about this, and I think there is also a bug in the existing .pause implementation. The current .pause implementation does not mask or defer window handler events when the user program is paused. The correct implementation might be to either queue up such events when paused, and release them once un-paused. In any case, when paused, window events should not result in continuation.